1. Field of the Invention
The present invention relates to a liquid sealed vibration isolating device for use in an engine mount for a motor vehicle, and more particularly, to the device which allows a hydraulic liquid passage such as a relief passage for restraining a cavitation phenomenon, to be opened and closed by utilizing the existing structure.
Further, the present invention relates particularly to the device which comprises an elastic diaphragm portion for absorbing internal pressure of a primary liquid chamber, and a stopper leg portion being integrally provided on and projecting from the elastic diaphragm portion, wherein deformation control of the elastic diaphragm portion is performed by the stopper leg portion.
2. Description of the Related Art
As a liquid sealed vibration isolating device of this type there is publicly known the device that a partition member for separating the primary liquid chamber and a secondary liquid chamber is provided with a damping orifice connecting the primary liquid chamber and the secondary liquid chamber and with a movable diaphragm for absorbing liquid pressure fluctuation of the primary liquid chamber.
Further, there is also publicly known the device that a leg portion a tip of which projects outward in a radial direction is formed on a lower surface (on the secondary liquid chamber side, and the same in the following description) of the movable diaphragm, wherein the tip of the leg portion is pressed against an inner surface of a circumferential wall provided on the support member of the movable diaphragm, and a lower portion of the circumferential wall is formed with a taper surface projecting toward the central side, so that at the time of large deformation of the movable diaphragm the leg portion is firmly compressed thereby to heighten the spring of the movable diaphragm (see a patent reference 1).
Moreover, the abrupt volume change of the primary liquid chamber creates large negative pressure (which means that the absolute value is large, and the same in the following description) within the primary liquid chamber, thereby generating bubbles in the hydraulic liquid. Then, there occurs the cavitation phenomenon which produces a noise when the bubbles burst. For restraining this phenomenon, there are provided, for example, a first orifice connecting the primary liquid chamber and the secondary liquid chamber and a second orifice connecting the secondary liquid chamber and another secondary liquid chamber which is partitioned by the movable diaphragm facing on the primary liquid chamber. When the large negative pressure is created, short-circuits are established through the second orifice and between the secondary liquid chamber and another secondary liquid chamber by the movable diaphragm which is elastically deformed to the primary liquid chamber side, so that the hydraulic liquid is allowed to flow through the second orifice and from the secondary liquid chamber to another secondary liquid chamber so as to control the negative pressure within the primary liquid chamber (see a patent reference 2).
Further, as the liquid sealed vibration isolating device of this type, there is known the one that the partition member for separating the primary liquid chamber and the secondary liquid chamber comprises the elastic diaphragm portion for absorbing the internal pressure of the primary liquid chamber, a frame member for supporting the elastic diaphragm portion, and the damping orifice which communicates between the primary liquid chamber and the secondary liquid chamber. The stopper leg portion is integrally formed on and projects from the elastic diaphragm portion. The tip of the stopper leg portion is pressed against the frame member to restrain the deformation of the elastic diaphragm, and the wall to which the tip of the stopper leg portion is pressed is formed with the taper surface. Therefore, as the displacement of the elastic diaphragm increases, the stopper leg portion is compressed by the frame member to increase the spring of the elastic diaphragm, so that the amount of the hydraulic liquid in the primary liquid chamber, which is supplied to the damping orifice passage, is increased so as to raise resonance efficiency of liquid column resonance thereby increasing the damping force (see the patent reference 1).    Patent reference 1: Japanese patent application laid open publication JP 2001-200882 A.    Patent reference 2: Japanese patent No. 4181171.